This invention relates to reinforced poly(ethylene terephthalate) compositions which can be extruded into sheets that are readily thermoformed at moderate pressures, below about 690 kPa, to give articles having well defined surface boundaries.
Polyethylene terephthalate has long been used as an injection-molding and extrusion resin for the fabrication of various articles for household or industrial use, including appliance parts, containers, and small auto parts. Because many of such articles must withstand considerable temperature changes and/or physical abuse, it is customary to blend poly(ethylene terephthalate) with other polymers which would improve its toughness and resistance to cracking. Additional improvement of its mechanical properties is obtained by reinforcement, especially with fibrous materials, principally with glass fibers. While many types of glass fiber-reinforced poly(ethylene terephthalate) compositions are available, they require the use of high pressure injection molding techniques. Typical of such compositions are those described in U.S. Pat. No. 4,124,561 to Phipps et al. Injection molding, normally carried out at about 20,000 to 100,000 kPa, requires considerably more energy than the conventional lower pressure operations such as, for example, thermoforming or hot sheet stamping, which are satisfactory for non-reinforced poly(ethylene terephthalate) compositions. Accordingly, it is very desirable to make available to the industry reinforced compositions capable of being formed into sheets that can be thermoformed at lower pressures, for example, from less than about 690 kPa to about 5520 kPa.
"Thermoforming" means fabricating in a single mold in which a sheet, at a temperature at least equal to the softening temperature but below the melting temperature of the resin from which it is made, is exposed on one side to a reduced pressure and on the other side to at least atmospheric pressure.